OPTOELECTRONICS AND ADVANCED MATERIALS – RAPID COMMUNICATIONS Vol. 12, No. 11-12, Nov.-Dec. 2018, p. 694 - 699

High efficient single stage Cuk LED driver for universal

input voltage applications with improved power quality

J. GNANAVADIVEL*, P. YOGALAKSHMI, N. SENTHIL KUMAR, S. MURALIDHARAN

EEE Dept., Mepco Schlenk Engineering College, Sivakasi, Tamilnadu, India

Bridgeless positive output Cuk LED driver operated under universal supply (90 V to 240 V) voltage for indoor applications with improved AC source power quality has been presented. The undesirable harmonic content in the supply current due to the operation of conventional diode bridge rectifier (DBR) based two stage LED driver is greatly reduced by the proposed single stage (bridgeless) LED driver with very simple control circuit. Therefore, high efficient operation along with low total harmonic distortion (THD) and high power factor can be acquired. Performance of the Cuk LED driver has been analysed under various LED load power provided with universal supply voltage in simulation study. Experimental results agree with the simulation results. The results guarantee the stable operation of LED driver with regulated DC link voltage and upgraded power quality satisfying IEC 61000-3-2 class C standards. (Received April 6, 2018; accepted November 29, 2018)

Keywords: Light Emitting Diode, Power factor, Source current harmonics, THD, Universal supply voltage

1. Introduction

LED lighting technology has become the most

attractive trend in the implementation of indoor/outdoor

lighting, commercial lighting, hospital lighting, residential

and traffic lighting, street/security lighting etc in the recent

days [1-2]. There are various key factors like prolonged

durability, eco-friendly, cost-effective, fast response, high

brightness, compact, improved luminous efficacy, low

power consumption has impressed many researchers to

choose LED lights in many applications [3]. A lot of

research works have been done for the improvement of

performance of LED light by improving its efficiency and

brightness [4-5].

But, few researchers focus on the eradication of power

quality issues on supply side while using LED lights. As

LED driver operates on DC voltage, an AC to DC

conversion stage is mandatory. For this purpose, a DBR

along with huge capacitor in order to produce pure DC is

most commonly employed. Fig. 1 shows the measured

THD and power factor (PF) with the relative source

current/voltage waveforms for DBR with bulk DC

capacitor set up. This assembly is used to pollute supply

current with very high harmonic distortions and produce

very low power factor [6]. Therefore, Power Factor

Correction [PFC] which contains a DC-DC converter

followed by DBR [two-stage conversion] must be needed

for improving power quality at AC source [7]. PFC must

be given much importance as all the loads connected to a

DC bus will be affected due to the impact of harmonic

polluted load connected to the same DC bus. Especially,

sensitive loads are fully got damaged and it leads to mal-

function of devices/equipment. Two –stage AC-DC LED

driver with converter topologies like flyback, buck, zeta,

Cuk, boost, SEPIC, three level boost converter are used as

PFC converters [8-15, 28-29].

Fig. 1. Measured THD and PF for DBR with

bulk capacitor

As per IEC 61000-3-2 class C standards, LED drivers

are enforced to maintain power factor value equal to [or]

greater than 0.9, with restricted source current THD at

supply side [14,18]. The convectional bridge rectifier for

DC-DC power converter topology provides better power

conditioning but it develops more conduction and

switching losses. During each conduction period, the

number of power devices are being turned ON is more

thereby efficiency gets lowered and hence cost of the

system increases. Electromagnetic interference (EMI) is

created due to generation of pulsating current from DBR.

High efficient single stage Cuk LED driver for universal input voltage applications with improved power quality 695

In order to overcome these limitations, bridgeless

single stage PFC converter topologies have been emerged

[18-25]. As only half of the total current is being passed

through the devices, bridgeless converter circuit minimizes

the conduction loss to a greater extent. Also, when

operated in DCM, control circuit becomes much simpler

since there exists only mono voltage loop. Thus, reduction

in number sensing parameters leads to cost-effective

control circuit. Moreover, DCM provides way for

achieving inherent power factors naturally [18]. Bridgeless

boost PFC converters have been developed which can

operate either in CCM/DCM. But the major issues

regarding boost type PFC is i) high start-up/overload in

rush current ii) magnitude of output voltage is always

higher than provided supply voltage [21]. Bridgeless buck

type PFC converters have been preferred as in [22]. Highly

distorted and irregular shaping of line current are the

serious drawbacks regarding buck PFC converter. Here,

magnitude of output voltage obtained is always lesser than

that of applied input voltage [23]. Regarding buck boost

type converters, bridgeless, SEPIC and Cuk PFC

converters have been used.

Number of research works using bridgeless SEPIC

rectifier with improved efficiency as in [26-27] are

applicable for low to high power applications. Yet, the

usage of very large inductance for suppressing inductor

current ripple restricts the usage of bridgeless SEPIC in

many sensitive applications. Unlike these buck, boost and

SEPIC rectifiers, Cuk PFC converters possess several

merits like very less input/output current ripples, very

small EMI filter, capable of withstanding high start

UP/overloads in rush current. Moreover, it is easier to

implement isolation [21,23]. Generally, Cuk converter

produces negative output voltage.

This paper presents the novel bridgeless type single

switch Cuk PFC converter fed LED driver for

indoor/outdoor lighting operated under universal supply

voltage. The proposed LED driver needs no inverse

amplifier circuitry for generation of positive load voltage.

A very simplified control circuitry with PI voltage

controller is provided to regulate LED load voltage. In

addition, reduced supply current harmonic distortion [ less

than 5%] with unity power factor is achieved. Hence,

regulated DC voltage for LED driver along with better

input side power quality is achieved using this single stage

proposed LED driver.

2. Circuit description

The power circuit of proposed single switch Cuk LED

driver with the schematic block diagram of simple control

circuit is presented in Fig. 2. The control circuit needs only

single parameter sensing as the Cuk LED driver operates

in DCM. An analogy is made between the desired LED

driver voltage and the measured LED driver voltage. The

difference in voltage is processed by PI controller to

generate gate pulse for MOSFET with the help of ramp

signal. The desired switching frequency is achieved by

proper ramp signal generation. With this simple control

circuit, the satisfactory results of improved power quality

(Less THD, High Power Factor) are acquired in the input

side AC supply. Rated LED power is 100 W. Rated AC

supply voltage is 120 V.

Fig. 2. Proposed single switch Cuk LED driver with the schematic control block diagram

The upcoming section describes the three operating

modes of Cuk LED driver.

3. Operation modes

The time period of ta – tb (as seen in Fig. 6)

corresponds to mode (a) as shown in Fig. 3. During this

time period (ta – tb), the diode Dp gets forward biased and

the current flows through the switch Swt and charge the

inductors Li2 and L01 with diode D2 ON. Hence, voltage

across both input and output inductors will be equivalent

to AC supply voltage.

696 J. Gnanavadivel, P. Yogalakshmi, N. Senthil Kumar, S. Muralidharan

Fig. 3. Mode I operation of Bridgeless Cuk LED driver

The corresponding current equations are,

i2

01

L s

i2

L s

01

di V (t)

dt L

di V (t)

dt L

The time period of tb – tc belongs to mode (b) as

shown in Fig. 4. During this mode, switch Swt is turned

OFF and the diodes D3 and Dp are turned ON, as the

inductors Li2 and L01 being discharged.

Fig. 4. Mode II operation of Bridgeless Cuk LED driver

The relative current equations are,

i2

01

L s

i2

L dr

01

di V (t)

dt L

di V

dt L

In the time period of tc – td ie., mode (c) as shown in

Fig. 5, both inductors Li2 and L01 act as sustained current

source and hence voltage across them will be ‘0’.

Freewheeling operation happens in this mode.

Fig. 5. Mode III operation of Bridgeless Cuk LED driver

Fig. 6. Theoretical Inductor current waveforms

of bridgeless Cuk LED driver

The components in the single stage Cuk LED driver

have been designed as per the following equations.

Output Voltage,

in m

dr in

V 2VV ; V

1 d

Input Inductors,

2

s dr

i1 i2

swt m dr

V IL L

2f V V

Output Inductor,

s dr dr

01

m drswt

V .I VL

2V V2 2 f

Input Capacitors,

dr

i1 i2 2

swt m dr

PC C

2f V V

High efficient single stage Cuk LED driver for universal input voltage applications with improved power quality 697

Output Capacitor,

dr

01

dr

IC

2 V

where, Vs – AC supply voltage, Vm – Maximum value of

AC supply voltage, fswt – Switching frequency, Vdr – LED

driver voltage, Idr – LED driver current, Pdr – LED driver

power, d – duty cycle. The design values of above

mentioned components of LED driver are tabulated in

Table 1.

Table 1. Ratings of Cuk LED driver components

Cuk LED Driver components Ratings

Input inductors (Li1, Li2) 5 mH

Output inductor (L01) 50 µH

Input capacitors (Ci1, Ci2) 220 nF

Output capacitor (C01) 2200 µH

4. Simulation study and analysis of CUK LED driver

The performance of the proposed LED driver under

universal supply voltage are analysed in both simulation

and experimental study. Supply voltage/ current

waveforms at 120 Vrms voltage under rated LED driver

voltage along with the corresponding FFT analysis of

input AC current is shown in Fig. 7 and Fig. 8.

Fig. 7. Supply voltage/ current waveforms at 120 V rms

voltage under rated LED driver voltage

With DCM operation, PF nearer to unity is intimately

achieved since both the source waveforms are in phase as

seen in Fig. 7.

Fig. 8. FFT analysis of input AC current (Vrms=120 V)

Fig. 9. Regulated LED driver voltage (Vrms=120 V)

Also, very less source current THD of 1.21% is

attained (as inferred from Fig. 8). Regulated LED voltage

of 48 V is obtained which is shown in Fig. 9. In the same

manner, supply voltage of 240 V is applied to the LED

driver and the relative waveforms and FFT analysis are

depicted in Fig. 10 and 11.

Fig. 10. Supply voltage/ current waveforms at 240 V rms

voltage under rated LED driver voltage

Improved power quality with 0.47% THD and unity

PF are obtained for the 240 V input supply voltage. Also,

well regulated LED driver voltage of 48 V is obtained in

this case as shown in Fig. 12.

Fig. 11. FFT analysis of input AC current (Vrms=240 V)

Fig. 12. Regulated LED driver voltage (Vrms=120 V)

698 J. Gnanavadivel, P. Yogalakshmi, N. Senthil Kumar, S. Muralidharan

The following graphical representation of supply

current THD values and the input PF values for wide range

of LED driver power under universal supply voltage

variations are shown in Fig. 13 and Fig. 14.

Fig. 13. Supply current THD values for wide range of LED

driver power under universal supply voltage variations

Fig. 14. Input PF values for wide range of LED driver

power under universal supply voltage variations

The obtained THD and PF values are within the IEC

61000-3-2 class C standards. At rated driver power, very

low THD values between 0.47 % and 1.61% are achieved

for 90 V to 240 V AC voltage variations. Also, PF values

range between 0.9868 and 1 which are almost closer to

unity is achieved for 90 V to 240 V variations of supply

voltage at rated LED driver power. Minimum value of

0.47 % THD with the maximum of 6.05 % is achieved for

different LED load power (100 W to 25 W) under

universal supply voltage variations (90 V to 240 V). PF

value of 0.9294 as minimum value with the maximum of

unity PF is achieved for different LED load power (100 W

to 25 W) under universal supply voltage variations (90 V

to 240 V). Thus, the proposed LED driver provides

enhanced power quality at ac mains. Regulated LED load

voltage of 48 V is obtained for all load power and supply

variations.

Fig. 15. Efficiency values for wide range of LED driver

power under universal supply voltage variations

Moreover, increased efficiency of 94.61 % is acquired

with this LED driver. The efficiency curve for different

load/supply variation is given in Fig. 15. Least efficiency

of 89.74% is achieved at supply voltage of 90 V at 25 W

LED load power and best efficiency of 94.61% is achieved

at supply voltage of 120 V at 100 W LED load power.

5. Experimental Verification of Cuk LED driver THD and PF values of 1.618%, 0.984% and 0.9921,

0.9994 are taken using power quality analyser for 120 V

and 240 V rms supply voltage at rated LED load power are

given in Fig. 17 and Fig. 18. Experimental AC

voltage/current waveforms are also given in Fig. 17 and

Fig. 18 respectively. The experimental driver voltage of 48

V is acquired for both supply voltages of Vrms equal to120

V and 240 V which can be seen from Fig. 19.

Fig. 16. Prototype of 100 W LED driver setup

Fig. 17. Experimental AC voltage/current waveforms

with relative power quality analysis (Vrms =120 V)

High efficient single stage Cuk LED driver for universal input voltage applications with improved power quality 699

Fig. 18. Experimental AC voltage/current waveforms

with relative power quality analysis (Vrms =240 V)

Fig. 19. Experimental LED driver voltage waveform

(Vrms =120 V, 240 V)

6. Conclusions

A new bridgeless Cuk LED driver with simple closed

control for universal supply voltage applications has been

presented in this paper. Poor power quality at input AC

supply due to LED driver is eradicated by proper control

circuit. Evaluation of Cuk LED driver for universal input

voltage (90 V – 240 V) under wide LED load power has

been analysed. Reduced supply current THD of 0.47% and

unity PF along with 94.61% efficiency are attained using

this single stage Cuk LED driver. Component ratings are

reduced to half the value as compared to conventional two

stage PFC converter. Due to DCM operation,

conduction/switching losses are greatly reduced and hence

efficiency gets improved. Experimental set up is built and

the results are validated with the simulation one.

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_______________________ *Corresponding author: jgvadivel@gmail.com,

gvadivel@mepcoeng.ac.in